With high integration of integrated circuits in recent years, formation of a pattern of a submicron order has been required. Excimer laser lithography has attracted special interest because it makes it possible to produce 64 MDRAM (mega-bit Dynamic RAM) and 256 MDRAM. Heretofore, near ultraviolet light has been mainly used for lithography. However, with the change of light source, the following performances have become required of the resist, in addition to various performances (e.g. heat resistance, film retention, profile, etc.) which have hitherto been required.
(a) The resist shall have high sensitivity to the above light source.
(b) The resist shall have high resolution.
Under these circumstances, a so-called chemical amplification type resist utilizing acid catalyst and chemical amplification effects has been suggested. The chemical amplification type resist develops a solubility of the exposed part to a developing solution by the reaction using an acid as a catalyst generated from an acid generator due to light irradiation, thereby obtaining a positive photoresist.
As the chemical amplification positive resist, a polyvinylphenol resin wherein the phenolic hydroxyl group is protected with a group which is eliminated by an action of the acid is often used. However, the resist using such a resin had a problem that it is liable to be influenced by the environment. It is well known that, in the process of proceeding the elimination reaction of a protective group due to a heat treatment after exposure (Post Exposure Bake, hereinafter sometimes referred to as "PEB"), the sensitivity changes with the temperature at the time of PEB and the performances change with the standing time before the heat treatment. The former is referred to as a "PEB dependence" and the latter is referred to as a "time delay effect". The time delay effect lowers the resolution and forms a layer insoluble to the developing solution on the surface of a resist film to form a T-shaped pattern after developing, which results in deterioration of the size reproducibility.
In order to prevent such a time delay effect, it is known to add a nitrogen-containing compound such as N-methyl-2-pyrrolidone to the chemical amplification type positive resist. However, even if N-methyl-2-pyrrolidone is added, it is not enough to prevent the time delay effect and the resolution is not sufficiently improved. Furthermore, the sensitivity of the resist is lowered due to the presence of the nitrogen-containing compound. Therefore, further improvement has been desired.
Under these circumstances, the present inventors have intensively studied so as to accomplish the following object.